JP3507713B2 - Light diffusing resin composition - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing plate and a light diffusing sheet, which have excellent light diffusing properties and light transmitting properties, and suppress the color difference generated in diffused light depending on the angle. Resin composition. The light diffusing resin composition of the present invention can be suitably used as a raw material for molded products such as light diffusing plates and light diffusing sheets used for TV screens, lighting covers, liquid crystal backlights and the like.

[Prior art]

Conventionally, there has been known a method of dispersing a light diffusing agent in a base resin in order to improve the light diffusing property of a light diffusing plate and a light diffusing film. Examples of such a light diffusing agent include: Inorganic fine particles such as titanium oxide and glass and crosslinked organic fine particles such as polymethylmethacrylate and polystyrene are used. However, when the inorganic fine particles are used as the light diffusing agent, there are various problems that the light transmittance is lowered, the mechanical damage during molding is easily caused, and the light is not uniformly diffused. In addition, when polymethylmethacrylate crosslinked fine particles are added as organic fine particles to a methylmethacrylate resin which is generally used as a base resin, the light transmittance is improved, but the difference in refractive index between them is reduced. Satisfactory light diffusion cannot be obtained. On the other hand, when polystyrene crosslinked fine particles are used as the organic fine particles, the light diffusivity is increased because the difference in the refractive index between the organic fine particles and the methyl methacrylate resin as the base resin is large, but the light emitted in the front direction is increased. However, there is a problem that the brightness decreases and the brightness decreases. Further, since the polystyrene crosslinked fine particles have a small Abbe number, the difference in Abbe number between the crosslinked fine particles and the methyl methacrylate resin as the base resin becomes large, and the diffused light causes a color difference depending on the viewing angle.

In Japanese Patent Laid-Open No. 10-67829, a crosslinked organic fine particle having a refractive index of about 1.50 to 1.53 is dispersed in a methyl methacrylate resin to have excellent light diffusing property and high front luminance. Light diffusing resins have been proposed.

Although such a light diffusing resin has improved light diffusivity and frontal brightness as compared with a resin in which polymethyl methacrylate or polystyrene crosslinked fine particles are dispersed in a methyl methacrylate resin, The diffusivity was not always satisfactory.

Therefore, in order to improve the light diffusibility, it is possible to increase the amount of organic fine particles proposed in the above publication, but if the amount of fine particles added is increased, the amount of light emitted in the front direction decreases. However, when it is used as a screen for a projection television, there is a problem in that the fineness and brightness of the image differ between when viewed from the front and when viewed obliquely from the front.

Further, in JP-A-54-155244, fluorine-based inorganic fine particles having a particle diameter of 1 to 10 μm having a refractive index of 0.01 to 0.1 from the refractive index of the base resin, or It is described that a light-diffusing resin having high light-diffusing property and high light-transmitting property can be obtained by dispersing a fluoride of polyacrylic acid ester in a base resin.

When the above-mentioned light-diffusing resin in which the fluorine-based inorganic fine particles are dispersed is used as a screen for a projection television, for example, although the light-diffusing property is high, a satisfactory light-transmitting property cannot be obtained and an image There is a problem that it gets dark. Further, the difference in refractive index from the base resin is 0.0
The light-diffusing resin in which the fluoride of polyacrylic acid ester of 1 to 0.1 is dispersed in the base resin has satisfactory light diffusing property and light transmitting property, but is seen from the front of the screen. There is a problem that the color is different between the case and the case viewed from an angle.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light diffusing resin composition which is excellent in light diffusing property and light transmitting property and does not cause color difference in diffused light depending on a viewing angle. .

[0009]

In order to solve the above problems, the present inventors have found that the difference between the Abbe number of the base resin and the organic resin having a lower refractive index than that of the base resin. They have found that it is effective to use fine particles as a light diffusing agent, and have completed the present invention.

Thus, the present invention provides a light diffusing resin composition in which organic fine particles as a light diffusing agent are dispersed in a base resin, wherein the organic fine particles are 10 to 80% by weight of a fluorine-containing alkyl (meth) acrylate monomer. % And vinyl monomer 90-2
It is spherical fine particles of a cross-linked vinyl copolymer copolymerized with 0% by weight and has an Abbe number of 5 or less with respect to the Abbe number of the base resin and has a refractive index higher than that of the base resin. A light diffusing resin composition having a low refractive index is provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The base resin used in the present invention is not particularly limited as long as it is usually used as a base resin for a light diffusing resin. For example, methyl (meth) acrylate is used. Examples of the resin include resins, alkyl (meth) acrylate resins such as ethyl (meth) acrylate resins and copolymers thereof, and alkyl (meth) acrylate-styrene copolymer resins. Among these, methyl methacrylate resin Is preferred.

The organic fine particles used in the present invention are spherical fine particles made of a crosslinked vinyl-based copolymer obtained by copolymerizing a fluorine-containing alkyl (meth) acrylate with a vinyl monomer in the presence of a crosslinking agent. Is.

As the fluorine-containing alkyl (meth) acrylate, for example, trifluoroethyl methacrylate,
Examples thereof include fluorine-containing alkyl methacrylate such as tetrafluoropropyl methacrylate and fluorine-containing alkyl acrylate such as perfluorooctylethyl acrylate.

The vinyl monomer copolymerizable with the fluorine-containing alkyl (meth) acrylate may be any vinyl monomer having a vinyl group, and specific examples thereof include alkyl methacrylate such as methyl methacrylate and butyl methacrylate. ,
Examples thereof include alkyl acrylates such as methyl acrylate and ethyl acrylate, and styrenes such as styrene and α-methylstyrene, and these can be used alone or in combination. For example, when the base resin is a methyl methacrylate resin, it is preferable to use methyl methacrylate having an Abbe number close to that of the base resin as the vinyl monomer.

The content of the fluorine-containing alkyl (meth) acrylate is preferably 10 to 80% by weight, more preferably 20 to 80% by weight, based on the total amount of the monomers. When the content of the fluorine-containing alkyl (meth) acrylate is less than 10% by weight, the difference in refractive index from the methyl methacrylate resin which is the base resin becomes small, and satisfactory light diffusibility cannot be obtained. Therefore, when this is used for a projection TV screen, the image in the front looks bright, but the image viewed obliquely becomes dark. When the fluorine-containing alkyl (meth) acrylate exceeds 80% by weight,
Methyl methacrylate resin as the base resin (Abbe number 5
When 7) is used, the difference in Abbe number between the two becomes large. Therefore, when this is used for a projection TV screen, a phenomenon occurs in which colors are different when viewed from the front of the screen and when viewed obliquely, which is not preferable.

The cross-linking agent used in the polymerization reaction is not particularly limited, but it is preferable to use one having two or more unsaturated groups, for example, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, etc. Functional dimethacrylate, trimethylolpropane trimethacrylate, divinylbenzene and the like can be mentioned. The polymerization reaction for producing the organic fine particles of the present invention may be either random copolymerization or block copolymerization.

The organic fine particles used in the present invention are spherical, and the weight average particle diameter is preferably 2 to 30 μm, more preferably 5 to 20 μm. If the weight average particle size is smaller than 2 μm, the methyl methacrylate resin composition obtained by dispersing the particle size selectively scatters light having a short wavelength, so that the transmitted light becomes yellowish, which is not preferable. Further, when the weight average particle diameter exceeds 30 μm, the light diffusion property of the methyl methacrylate resin composition obtained by dispersing the particle decreases, and the particles are visually recognized as a foreign substance when light passes through the resin. Not preferable.

The organic fine particles used in the present invention are
It has an Abbe number of 5 or less with respect to the Abbe number of the base resin, preferably 4.0 or less. If the difference in Abbe number exceeds 5, it is not preferable when used as a screen for a projection television, for example, the color of the image changes depending on the position where the screen is viewed. Therefore, although the Abbe number of the organic fine particles varies depending on the Abbe number of the base resin, it is generally preferable that the organic fine particles have an Abbe number of 58 to 62.

The Abbe number is a constant indicating the degree of dispersion of the optical glass. The smaller the difference in refractive index due to the change in the wavelength of light, the higher the Abbe number, and the smaller the difference in color due to the light of the substance. The Abbe's number is measured using a refractometer capable of measuring the refractive index of a solid by using light sources (486n) having different wavelengths.
m, 589 nm, 656 nm) is measured and calculated by the following equation.

[0020]

[Equation 1]

For example, a fluorine-containing (meth) acrylic acid ester resin has a high Abbe number, and a homopolymer is 65 to 7
The range is 0 (for example, the Abbe number of trifluoroethyl methacrylate is 67). In the case of a projection TV screen in which a light diffusing agent having a refractive index different from that of the base resin is dispersed in the base, the smaller the difference in Abbe number between the base resin and the light diffusing agent, the difference in color depending on the viewing angle. Becomes smaller.

The organic fine particles used in the present invention may be those having a refractive index lower than that of the base resin. When the refractive index is larger than that of the base resin, the resulting light diffusion plate or sheet has a low amount of transmitted light,
Further, the obtained screen cannot provide a satisfactory viewing angle. Further, it is preferable that the difference in refractive index between the base resin and the organic fine particles is neither too small nor too large. For example, when the methyl methacrylate resin as the base resin has a refractive index of 1.495, the refractive index is 1.42.
When smaller organic fine particles or organic fine particles having a refractive index larger than 1.51 are used, the difference in refractive index from the base resin is too large, so that the light diffusivity is improved, but the light transmittance in the front direction is increased. It becomes low, which is not preferable. When organic fine particles having a refractive index of 1.48 to 1.51 are used, the difference in refractive index from the methyl methacrylate resin as the base resin is too small, and it is difficult to obtain satisfactory light diffusibility.

From the above, it is preferable that the organic fine particles have a refractive index lower by 0.015 to 0.075 than the refractive index of the base resin. Specifically, when the base resin is a methyl methacrylate resin having a refractive index of 1.495, the organic fine particles preferably have a refractive index of 1.42 to 1.48.

The organic fine particles in the present invention are added when a base resin is extruded or injection-molded, and once masterbatched, a plate made of a light-diffusing resin composition or a light-diffusing resin composition obtained by cast molding. And film and its processed products. The addition ratio of the organic fine particles to the base resin is not particularly limited, but is usually preferably 0.5 to 10.0% by weight, and more preferably 1.0 to 7.0% by weight.

The thermal decomposition start temperature of the organic fine particles (the temperature at which the resin is reduced by 3% due to heat) is preferably equal to or higher than the molding temperature of the resin. For example, the molding temperature of a methyl methacrylate resin is generally 220 to 260 ° C., but considering that the resin temperature rises to 280 ° C., the thermal decomposition start temperature of the organic fine particles is preferably higher than 280 ° C. When the thermal decomposition start temperature of the organic fine particles is low, molding defects such as silver streaks are likely to occur during molding of the light diffusing resin composition, which is not preferable.

[0026]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited thereto. In addition, "part" in the following examples means a weight part.

Example 1 [Production of organic fine particles] In a 2 liter container, 20 parts of tricalcium phosphate, which is sparingly soluble in water, 1200 parts of water and 1 part of sodium lauryl sulfate.
I put in a section. Separately, 260 parts of methyl methacrylate, 20 parts of ethylene glycol dimethacrylate, and 120 parts of trifluoroethyl methacrylate are placed in a 1-liter container.
Parts, cumene peroxide 2 parts and normal dodecyl mercaptan 2 parts were added to prepare a monomer solution. This monomer solution was placed in the above-mentioned 2 liter container, mixed, and stirred at high speed with a homomixer to disperse. Particle size is 10
When it reaches about μm, put it in a jacket-type 2 liter autoclave equipped with a stirrer and stir it 7
Polymerization was carried out at 0 ° C. for 5 hours and 100 ° C. for 5 hours. The obtained dispersion was filtered, washed, dehydrated and dried to obtain organic fine particles. The obtained organic fine particles have a weight average particle diameter of 8.7.
μm, the thermal decomposition starting temperature was 292 ° C.

The weight average particle diameter is measured by a Coulter counter (manufactured by Coulter Co.), and the thermal decomposition start temperature is measured by a thermoanalyzer TG-40 (manufactured by Shimadzu Corp.), at which the temperature at which the weight is reduced by 3% by heat did.

2,2-azobis-2,4 was added to 100 parts of a monomer mixture (65 parts of methyl methacrylate, 5 parts of ethylene glycol dimethacrylate, 30 parts of trifluoroethyl methacrylate) having the same composition as the organic fine particles.
1 part of dimethylvaleronitrile was dissolved. This melt was poured into a glass mold having a size of 100 mm × 50 mm and t = 1 mm, the temperature was raised from 40 ° C. to 80 ° C. over 5 hours for polymerization, and further 100 ° C. for 1 hour. After cooling the obtained polymer, it was peeled from the glass mold to obtain a refractive index test piece. The refractive index is RX-2000 manufactured by Atago, and the Abbe number is Abbe refractometer 2 manufactured by Atago.
It was measured using T. The refractive index is 1.465,
The Abbe number was 59.0.

[Production of Light-Diffusing Resin Composition and Light-Diffusing Plate] Organic fine particles obtained by the above-mentioned method were treated with methyl methacrylate resin (Sumitomo Chemical Co., Ltd .: MG-5, refractive index 1.495, Abbe number). 57%) to 3% by weight,
After blending, the mixture was supplied to an extruder to produce a pellet-shaped light diffusing resin composition. The pellets were supplied to an injection molding machine and injection-molded to obtain a light diffusion plate having a size of 100 mm × 50 mm and t = 2 mm. By projecting from the back side of this light diffusion plate with a projector, the difference in color between when viewed from the front and when viewed obliquely was examined.

The light diffusing property and light transmitting property of the obtained light diffusing plate were measured using an automatic goniophotometer (GP-200 manufactured by Murakami Color Research Laboratory Co., Ltd.) at 0 ° (front direction). ~ 90
For each angle of °, the relative transmitted light intensity at each angle was measured with the transmitted light intensity in the 0 ° direction as 100.

The light diffusivity index is expressed as the degree of dispersion. The degree of dispersion refers to the angle at which the transmitted light intensity reaches 50 when the transmitted light intensity when light is applied to the light diffusion plate from the front direction (0 °) is 100. Table 1 shows the refractive index, the Abbe number, the relative transmitted light intensity, and the dispersity measured as described above.

Since the light diffusivity and the light transmissivity vary depending on the thickness of the light diffusing plate and the amount of the light diffusing agent, the thickness of the measuring piece of the light diffusing plate is 2 mm, and the addition amount of the organic fine particles is based on the base resin. Based on 3 wt%.

Examples 2 to 5 Examples except that the organic fine particles produced in Example 1 were added to the methyl methacrylate resin at 1.0, 2.0, 2.5 and 5.0% by weight, respectively. A light diffusing resin composition and a light diffusing plate were obtained in the same manner as in 1. Table 1 shows the relative transmitted light intensity, the refractive index, the Abbe number and the degree of dispersion of the light diffusing plate obtained in each example.

Example 6 Organic fine particles were produced in the same manner as in Example 1 except that the amount of methyl methacrylate was changed to 180 parts and the amount of trifluoroethyl methacrylate was changed to 200 parts. The obtained organic fine particles had a weight average particle diameter of 7.9 μm and a thermal decomposition initiation temperature of 293 ° C. Then, a light diffusing resin composition and a light diffusing plate were manufactured in the same manner as in Example 1. Table 1 shows the relative transmitted light intensity, refractive index, Abbe number, and dispersity of the obtained light diffusing plate.

Comparative Example 1 Organic fine particles were produced in the same manner as in Example 1 except that styrene was used instead of trifluoroethyl methacrylate. The obtained organic fine particles had a weight average particle diameter of 8.5 μm and a thermal decomposition initiation temperature of 293 ° C. Next, a light diffusing resin composition and a light diffusing plate were manufactured in the same manner as in Example 1 except that 2% by weight of the obtained organic fine particles was added to the methyl methacrylate resin. Table 1 shows the relative transmitted light intensity, refractive index, Abbe number, and dispersity of the obtained light diffusing plate.

Comparative Examples 2 to 5 Examples except that the organic fine particles produced in Comparative Example 1 were added to the methyl methacrylate resin at 1.0, 2.5, 3.0 and 5.0% by weight, respectively. A light diffusing resin composition and a light diffusing plate were obtained in the same manner as in 1. Table 1 shows the relative transmitted light intensity, refractive index, Abbe number and dispersity of the obtained light diffusion plate.
Shown in.

Comparative Example 6 Organic fine particles were produced in the same manner as in Example 1 except that 180 parts of methyl methacrylate and 200 parts of styrene were used instead of trifluoroethyl methacrylate. The obtained organic fine particles have a weight average particle diameter of 8.6μ.
m, and the thermal decomposition starting temperature was 291 ° C. Then, a light diffusing resin composition and a light diffusing plate were manufactured in the same manner as in Example 1. Table 1 shows the relative transmitted light intensity, refractive index, Abbe number, and dispersity of the obtained light diffusing plate.

Comparative Example 7 Organic fine particles were produced in the same manner as in Example 1 except that the amount of methyl methacrylate was 360 parts and the amount of trifluoroethyl methacrylate was 20 parts. The obtained organic fine particles had a weight average particle diameter of 8.1 μm and a thermal decomposition initiation temperature of 290 ° C. Then, a light diffusing resin composition and a light diffusing plate were manufactured in the same manner as in Example 1. Table 1 shows the relative transmitted light intensity, refractive index, Abbe number, and dispersity of the obtained light diffusing plate.

Comparative Example 8 Instead of the organic fine particles produced in Example 1, silicone fine particles (Tospearl 2000B: Toshiba Silicone, average particle diameter 6.2 μm, refractive index 1.435, Abbe number 6) were used.
A light diffusing plate was obtained in the same manner as in Example 1, except that 7% was added to methyl methacrylate resin in 7). Table 1 shows the relative transmitted light intensity, refractive index, Abbe number, and dispersity of the obtained light diffusing plate.

Comparative Example 9 Example 1 except that the amount of methyl methacrylate was 0 parts and the amount of trifluoroethyl methacrylate was 380 parts.
Organic fine particles were produced in the same manner as in. The obtained organic fine particles had a weight average particle diameter of 7.5 μm and a thermal decomposition initiation temperature of 285 ° C. Then, a light diffusing resin composition and a light diffusing plate were manufactured in the same manner as in Example 1. Table 1 shows the relative transmitted light intensity, refractive index, Abbe number, and dispersity of the obtained light diffusing plate.

[0042]

[Table 1]

From Table 1 above, when the difference in Abbe number between the base resin and the organic fine particles is large, when projected from the back side of the light diffusing plate by the projector, the color seen from the front direction and the oblique (angle difference 60 It can be seen that there is a difference in the color viewed from the () direction. For example, Comparative Examples 1, 6, 8 and 9 all had a difference in Abbe number of more than 5, and a difference in color depending on the viewing angle was confirmed. Further, it is understood that when the difference in the refractive index between the base resin and the organic fine particles is extremely small, the light diffusing property becomes small. For example, in Comparative Example 7 in which the difference in refractive index is 0.005, the amount of organic fine particles added to the substrate is 3%, but the dispersity is only 1 °.

From the results of Examples 1 to 5 and Comparative Examples 1 to 5, it is understood that the light diffusivity is excellent when the refractive index of the organic fine particles is lower than that of the base resin. Further, in Table 2 and FIG. 1, based on the results obtained in Examples 1 to 5 and Comparative Examples 1 to 5, the addition amount of organic fine particles and the front direction (0 °)
Of the transmitted light intensity.

[0045]

[Table 2]

From Table 2 and FIG. 1, it can be seen that the transmitted light intensity decreases as the amount of organic fine particles added increases. Also, from FIG. 1, the refractive index of the base resin (1.495)
It can be seen that the organic fine particles having a lower refractive index have higher transmitted light intensity than those having a higher refractive index than the base resin.

[0047]

The light diffusing plate manufactured from the light diffusing resin composition in which the organic fine particles of the present invention are dispersed is a lighting cover,
It is effective in fields requiring high light diffusivity and light transmission, such as light diffusing plates for liquid crystal backlights and screens for projection televisions, and has the advantage that it looks bright over a wide angle and diffuses depending on the viewing angle. There is also an effect that there is no color difference in light.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of organic fine particles added and transmitted light intensity, and the relationship between the refractive index of organic fine particles and transmitted light intensity.

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Claims (2)

(57) [Claims] 1. A light-diffusing resin composition in which organic fine particles as a light diffusing agent are dispersed in a base resin made of a methyl methacrylate resin, wherein the organic fine particles are fluorine-containing alkyl (meth) acrylate monomer 10. To 80% by weight and 90 to 20% by weight of a vinyl monomer are fine particles of a crosslinked vinyl-based copolymer, and have an Abbe number of 5 or less from the Abbe number of the base resin. A light diffusing resin composition having a refractive index of 0.015 to 0.075 lower than that of the base resin. 2. The organic fine particles have an Abbe number of 58 to 62 and a refractive index of 1.42 to 1.48.
The light diffusing resin composition described in 1.